Lorenz 96 2-scale ================= Overview -------- The Lorenz 96 2-scale model was first described by Edward Lorenz during a seminar at the European Centre for Medium-Range Weather Forecasts in the Autumn of 1995, the proceedings of which were published as Lorenz (1996) [1]_ the following year, hence the model is commonly referred to as Lorenz 96. The model state varies on two separate time scales, one for the X dimension and another in the Y dimension. It is constructed by coupling together two implementations of the Lorenz 96 single-scale model. The constant *F* term in Lorenz 96 single-scale model is replaced by a term that couples the two scales together. Lorenz 96 2-scale is a widely studied model because the differing timescales can be viewed as an analog of processes that occur on different time and spatial scales in the atmosphere such as large-scale flow and localized convection. The `references`_ contain some of the earlier studies including Palmer (2001), [2]_ Smith (2001), [3]_ Orrell (2002), [4]_ Orrel (2003), [5]_ Vannitsem and Toth (2002), [6]_ Roulston and Smith (2003), [7]_ and Wilks (2005). [8]_ The Lorenz 96 2-scale model has a ``work/workshop_setup.csh`` script that compiles and runs an example. This example may be explored in the :doc:`DART tutorial <../../theory/readme>` and is intended to provide insight into model/assimilation behavior. The example **may or may not** result in good (*or even decent!*) results! Development History ~~~~~~~~~~~~~~~~~~~ This DART model interface was developed by Josh Hacker as an adaptation of the Lorenz 96 implementation. The 2-scale model is the second model described in Lorenz (1996). Quick Start ----------- To run Lorenz 96 2-scale with its default settings: 1. Ensure you have the correct settings in mkmf.template in ``/build_templates/mkmf.template`` 2. Build the DART executables using the ``quickbuild.sh`` script in the ``./work`` directory. 3. Once the executables have been built, the two Perl scripts provided in the ``./shell_scripts`` directory, ``spinup_model.pl`` and ``run_expt.pl``, can be used to spin up the model and run an experiment. Namelist -------- The model also implements the variant of Smith (2001), which can be invoked by setting ``local_y = .true.`` in the ``&model_nml`` namelist in the ``input.nml`` file. The ``&model_nml`` namelist is read from the ``input.nml`` file. Namelists start with an ampersand ``&`` and terminate with a slash ``/``. Character strings that contain a ``/`` must be enclosed in quotes to prevent them from prematurely terminating the namelist. .. code-block:: fortran &model_nml model_size_x = 36, y_per_x = 10, forcing = 15.00, delta_t = 0.005, coupling_b = 10.0, coupling_c = 10.0, coupling_h = 1.0, local_y = .false., time_step_days = 0, time_step_seconds = 3600 template_file = 'filter_input.nc' / Description of each namelist entry ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-------------------+--------------------+-------------------------------------+ | Item | Type | Description | +===================+====================+=====================================+ | model_size_x | integer | Number of variables in x-dimension. | +-------------------+--------------------+-------------------------------------+ | y_per_x | integer | Scaling factor for number of | | | | variables in y-dimension compared | | | | to x-dimension. | +-------------------+--------------------+-------------------------------------+ | forcing | real(r8) | Forcing, F, for model. | +-------------------+--------------------+-------------------------------------+ | delta_t | real(r8) | Non-dimensional timestep. This is | | | | mapped to the dimensional timestep | | | | specified by time_step_days and | | | | time_step_seconds. | +-------------------+--------------------+-------------------------------------+ | coupling_b | real(r8) | | +-------------------+--------------------+-------------------------------------+ | coupling_c | real(r8) | | +-------------------+--------------------+-------------------------------------+ | coupling_h | real(r8) | | +-------------------+--------------------+-------------------------------------+ | local_y | boolean | | +-------------------+--------------------+-------------------------------------+ | time_step_days | integer | Number of days for dimensional | | | | timestep, mapped to delta_t. | +-------------------+--------------------+-------------------------------------+ | time_step_seconds | integer | Number of seconds for dimensional | | | | timestep, mapped to delta_t. | +-------------------+--------------------+-------------------------------------+ | template_file | character(len=256) | this in script | +-------------------+--------------------+-------------------------------------+ References ~~~~~~~~~~ .. [1] Lorenz, Edward N., 1996: Predictability: A Problem Partly Solved. *Seminar on Predictability*. **1**, ECMWF, Reading, Berkshire, UK, 1-18. .. [2] Palmer, Timothy N., 2001: A nonlinear dynamical perspective on model error: A proposal for non‐local stochastic‐dynamic parametrization in weather and climate prediction models. *Quarterly Journal of the Royal Meteorological Society*, **127**, 279–304. https://doi.org/10.1002/qj.49712757202 .. [3] Smith, Leonard A., 2001: Disentangling uncertainty and error: On the predictability of nonlinear systems. *Nonlinear dynamics and statistics,* Alistair I. Mees, Editor, Birkhauser, Boston, USA, 31–64. .. [4] Orrell, David, 2002: Role of the metric in forecast error growth: How chaotic is the weather? *Tellus*, **54A**, 350–362. .. [5] Orrell, David, 2003: Model error and predictability over different timescales in the Lorenz '96 Systems. *Journal of the Atmospheric Sciences*, **60**, 2219–2228. .. [6] Vannitsem, Stéphane and Zoltan Toth, 2002: Short-term dynamics of model errors. *Journal of the Atmospheric Sciences*, **59**, 2594–2604. .. [7] Roulston, Mark S. and Leonard A. Smith, 2003: Combining dynamical and statistical ensembles. *Tellus*, **55A**, 16–30. .. [8] Wilks, Daniel S., 2005: Effects of stochastic parametrizations in the Lorenz ’96 system. *Quarterly Journal of the Royal Meteorological Society*. **131**. 389-407. https://doi.org/10.1256/qj.04.03